Testing for porosities in the hermetic sealing of food packaging

Using containers made of paperboard coated with polyethylene and aluminium foils (aseptic carton) is common practice for packaging beverages such as milk or fruit juices. But even tiny defects in the packaging coating systems can lead to spoilage of the product inside.

Beverage cartons must be hermetically sealed, solid, and must extend the shelf life of the contained product by shielding them from light and germs. Depending on the contents, various coating systems are used atop a paperboard base. To protect beverages against oxidation, an aluminium foil is used, while polyethylene foil in turn protects the aluminium against corrosion by acidic liquids such as fruit juices

It is crucial that the polyethylene foil is completely sealed; otherwise, corrosion of the aluminium foil is unavoidable. A well established, simple and effective method to test for the presence of gaps in the polyethylene layer is to use a porosity tester, also called a ‘holiday detector’.

FISCHER’s new POROSCOPE® HV5, equipped with a roller electrode, is ideal for monitoring the continuity of the polyethylene coating that protects the aluminium foil in aseptic carton packaging. The test method is based on the fact that all electrically insulating coating materials have a much higher disruptive strength than air does.

Operation is simple and can be performed by non-technical staff: the test voltage is set on the POROSCOPE® according to the disruptive strength and thickness of the innermost polyethylene layer. Alternatively, a test standard can be selected and a coating thickness can be set. The POROSCOPE® automatically adjusts for the appropriate high voltage. The specimen is grounded and then the electrode is moved slowly across its surface. The voltage drops briefly when the electrode passes a defective spot; a spark-over, accompanied by optical and acoustic signals, indicates the presence of a pore.

Fig.1: POROSCOPE® HV5 with roller electrode

Besides being easy to use, the POROSCOPE® is also compact and lightweight, making it an indispensable portable companion for anyone tasked with quality control on multi-coated food packaging.

The new FISCHER POROSCOPE® HV 5 with roller electrode is perfectly suited for performing the porosity testing required by the food packaging industry. For further information please contact your local partner for FISCHER products.